So I did an experiment here recently. I wanted to see if the heavy wall 18.5" barrel and the magazine tube with S&J +2 extension from off my 590a1 would fit my Mossberg 500. They mated up perfectly. So I have sold my 500 ghost ring barrel and 5 shot tube and spring on eBay. I've since purchased a Mossberg 835 five shot magazine tube part number 12113p and the Mossberg 835 spring # 12194. I also ordered an s&j hardware mag extension. The mag tube came in as did the spring. I test fitted them when the +2 extension arrived from Canada. I initially tried the s&j follower and spring an was only able to get 6 in the magazine tube. I thought I'd try the 5 round Mossberg 500 spring. Then it hit me and I compared the 835 spring to the 500 spring and it was longer than the 500 but not as long as the s&j spring. So I assembled it all and was able to load 7 rounds of estate and sellier and bellot in the tube no issues. I tested several various brand rounds they all seemed to cycle fine and the s&j delrin follower and the 835 spring load smooth as butter!

I've also purchased the longer slide action assembly and nut and will be putting a magpul moe forend on it.
For those curious I did use my law enforcement discount to get these parts at a discounted rate. Long action tube assembly part # is 11603bl and the tube nut is 3408.

I'm just waiting for my 18.5" accuchoke heavy wall barrel to get here and then I'll install it.

I wanted this setup like my 590a1.

I'm gonna be keeping the Mesa tactical stuff and putting it on a maverick 88 project in the future.

I plan on having the Accu choke barrel magnaported like my 590a1 and the forcing cone lengthened, polished, and the barrel back bored by Aimpro tactical like I did on my 590a1. I'll be running an improved cylinder choke on it like my 590a1.

I do plan on purchasing the aluminum trigger group for this one.

Who else has an 8 shot Mossberg 500 with 18.5" barrel? Please chime in if you do.

Mossberg sent me the accuchoke barrel finally for my Mossberg 590a1. What they neglected to tell me before I ordered it was that they'd changed things mid production on the 50774 model. They no longer came with the five shot mag tube and thus the S&J hardware extension does not work now. So now I have a 90.00 paperweight for a mag extension.

So Mossberg is supposedly sending me a 6 round magazine tube for this. It'll look like the pic below and I'll no longer be able to have an 8 shot 18.5" barrel. This irritates the hell out of me. It does not look aesthetically pleasing as the mag tube won't be flush with the barrel. I guess when I get it I'll measure and see how much room I have and see if I can find a +1 extension to the exact dimensions needed. If not I may see if a gunsmith can work something up and cut down a 2 round extension and make it work.

Of course my 500 will have a magpul sga stock and magpul moe forend.

This whole experience has soured me on Mossberg. They just kept screwing up and serving me the wrong parts. Then I wait 4 weeks for a damn barrel that's totally different than what I wanted or requested. I'll not be buying anymore Mossberg products ever and will discourage as many as I can from doing the same.

I guess I'll be selling my Mesa tactical stuff and not be building a maverick 88 after all as I cannot build it the way I want it.

One of my major gripes with the M500 has always been the mag tube/barrel thing. Whatever mag tube you have is pretty much what you're stuck with (oh, it CAN be removed and replaced, but it's a bit of a PITA) whereas with M870 you can change mag tube extensions like you change your socks if the mood strikes you, with no affect on your barrel. The extended mag M500 MUST have dedicated barrels, and the choice of them is very limited.

I have three M500s--one with extended tube, two without--and then one day about 10 years ago I decided I was worth the best, dammit, and bought myself a nice 1950s 870 Wingmaster. Which happens to be wearing an extended mag at the moment.